Such apparatus can be used in refractive ophthalmology for correction of the eyesight defect to cut a corneal lamella, which can be unilaterally detached from the corneal surface and folded aside. In this case, such apparatus is frequently referred to also as a laser keratome, which is used in the so called LASIK operation (laser in situ keratomileusis) to expose the corneal tissue by cutting the above-described corneal lamella (which is also called a flap).
In the LASIK operation, a defined corneal volume is then ablated, after cutting and folding open the flap, by means of an excimer laser, which is a different laser than the one used for cutting the flap. Subsequently, the flap is folded back down so that the profile of the anterior corneal surface is altered due to the removed corneal tissue according to the desired correction of ametropia.
On the one hand, such an approach for correction of ametropia leads to the use of two different lasers. On the other hand, the control of the excimer laser to remove the cornea is difficult and has to be carried out with extremely high precision.
In view thereof, it is the object of the invention to provide an apparatus for generating a correcting cut surface in the cornea of an eye so as to correct ametropia, by which apparatus the desired correcting cut surface can be easily achieved with high precision.
The object is achieved by an apparatus for generating a correcting cut surface in the cornea of an eye so as to correct ametropia, said apparatus comprising a laser unit, which can focus and move pulsed laser radiation in the cornea to generate a cut surface; a first contact element; and a control unit, which controls the laser unit to generate a cut surface and which has a standard setting which, when a standard curvature is imposed upon the anterior corneal surface by the first contact element, would lead to a standard cut surface in the cornea having a known curvature with respect to a reference surface, wherein the curvature, with respect to the reference surface, of the correcting cut surface to be generated deviates from the known curvature of the standard cut surface which can be generated, and said apparatus comprises a second contact element adapted to generate the correcting cut surface, which second contact element, when in contact with the anterior corneal surface, imposes upon the latter an actual curvature deviating from the standard curvature, and thus has the effect that generating a cut surface using the standard setting results in the correcting cut surface to be generated.
Thus, in the apparatus according to the invention, a cut surface is generated using the standard setting of the control unit, which facilitates operation of the apparatus. Determination of the profile of the correcting cut surface is realized by the individually adapted second contact element. Therefore, it is only required to adapt the contact element in accordance with the correcting cut surface to be generated for the desired correction of ametropia.
In particular, this enables the use of a conventional laser keratome for flap-cutting in order to generate the correcting cut surface, without requiring any change in the control of the laser unit. It is only required to provide the correspondingly adapted second contact element which imposes the actual curvature upon the anterior corneal surface.
The reference surface, is, for example, the surface which coincides with the anterior corneal surface before the cut surface is generated, in which case the cornea is not in contact with any of the contact elements and has its natural profile.
The second contact element may be provided such that, due to the imposed actual curvature alone, it has the effect that generating the cut surface using the standard setting results in the correcting cut surface to be generated. Thus, due to the imposed actual curvature, the cornea is deformed such that the standard cut surface coincides with the correcting cut surface to be generated. Such second contact element is particularly easy to produce.
In particular, the second contact element and/or the first contact element may have a refractive index adapted to the refractive index of the eye's cornea.
The second contact element, however, can also be provided such that the second contact element has a further optical property which also contributes to generating the correcting cut surface. Said property may be, for example, refraction and/or diffraction.
The second contact element can be provided such that the deviation between the actual curvature given by the second contact element and the standard curvature given by the first contact element corresponds to the deviation between the correcting cut surface and the standard cut surface. Such a contact element is easy to produce. The first contact element, for example, may comprise a spherically curved contact surface and the standard setting may be such that a flap having a constant thickness relative to the anterior corneal surface can be generated using the first contact element.
The second contact element may have a one-part design. However, it is also possible for the second contact element to comprise a main part, having a first contact surface, and an adapting element, which is connected with the first contact surface and comprises a second contact surface facing away from the first contact surface, the spatial shape of said second contact surface being selected such that the actual curvature can be imposed upon the cornea.
Due to this two-part design, particularly the main part of the second contact element can be used several times and the adaptation can be effected exclusively via said adapting element.
The main part may have the same design as the first contact element.
The adapting element may be provided as a sheet or a lens, which may be, for example, preformed sheets or lenses. It is also possible to individually adapt the sheets or lenses, respectively.
The correcting cut surface may be selected such that a corneal flap is separated from the cornea thereby, so that the curvature of the anterior corneal surface is modified accordingly.
It is also possible for the correcting cut surface to separate one side of a corneal lenticle (small corneal volume) from the surrounding corneal material. In this case, a further cut surface is generated, using the standard setting, by means of the apparatus and the first contact element or a further contact element contacting the anterior corneal surface, so as to generate a further correcting cut surface within the cornea, which, together with the correcting cut surface generated with the second contact element, completely separates the corneal lenticle from the surrounding cornea.
According to this approach, it is preferred to first generate the correcting cut surface located at a greater depth (i.e. at a greater distance from the anterior corneal surface). In particular, the correcting cut surface located at a greater depth may have a curvature relative to the anterior corneal surface, differing from that of the anterior corneal surface. The correcting cut surface located higher up may be provided, in particular, as a flap at a constant distance from the anterior corneal surface.
The apparatus may further comprise at least a third contact element, which imposes a further curvature upon the anterior corneal surface when contacting the latter, said further curvature deviating from the standard curvature as well as from the actual curvature of the second contact element, and thus has the effect that a cut surface generated using the standard setting results in a further correcting cut surface.
Further, the contact surface of the corresponding contact element defining the actual curvature may be flexible. Said flexibility is selected such that, although on average the actual curvature is imposed upon the anterior corneal surface, minor irregularities can be compensated for. This has the advantageous effect that the correcting cut surface to be generated has an extremely smooth profile. Said flexibility may be achieved, for example, by a thin, flexible layer (e.g. a gel layer) forming the contact surface, which is in turn applied to a contact element carrier that is rigid with respect to the cornea.
The contact elements may be made, for example, from glass or plastics.
The correcting cut surface may serve to correct myopia, hyperopia or other eyesight defects.
Further, a contact element for an apparatus for generating a correcting cut surface in the cornea of an eye so as to correct ametropia is provided, said apparatus comprising a laser unit which can focus and move pulsed laser radiation in the cornea to generate a cut surface; a standard element, and a control unit, which controls the laser unit to generate a cut surface and which has a standard setting which, when a standard curvature is imposed upon the anterior corneal surface by the standard element, would lead in the cornea to a standard cut surface having a known profile relative to a reference surface, wherein the curvature, with respect to the reference surface, of the correcting cut surface to be generated deviates from the known curvature of the standard cut surface which can be generated, and wherein the contact element, when contacting the anterior corneal surface, imposes upon the latter an actual curvature deviating from the standard curvature and, thus, has the effect that generating a cut surface by means of the apparatus using the standard setting results in the correcting surface to be generated.
For example, such a contact element allows to generate the desired correcting cut surface by means of a conventional laser keratome, without having to modify the control of the laser unit. It is only required to replace the standard element with the contact element according to the invention. Thus, the curvature of the correcting cut surface is given by the individually adapted contact element.
In particular, the contact element has the effect that, due to the imposed actual curvature alone, the cut surface generated using the standard setting results in the correcting cut surface to be generated. Such a contact element is particularly easy to produce.
Thus, the deviation between the actual curvature given by the contact element and the standard curvature given by the standard element may correspond to the deviation between the correcting cut surface and the standard cut surface. The contact element may have a one-part design. It may consist of transparent glass or transparent plastics. In particular, the refractive index of the contact element is adapted to the refractive index of the cornea.
As an alternative, the contact element may comprise a main part having a first contact surface and an adapting element, which is connected with said first contact surface and comprises a second contact surface facing away from the first contact surface, the spatial shape of said second contact surface being selected such that the actual curvature can be imposed upon the cornea. The adapting element may be provided as a sheet or as a lens. In such a two-part contact element, the main part, for example, may be re-used, in which case only the adapting element has to be replaced.
In the contact element, the contact surface defining the actual curvature can be flexible with respect to the cornea. However, said flexibility is selected such that on average the desired actual curvature can be imposed. This can be realized, for example, by providing the contact surface as a thin, flexible layer which is applied onto a rigid contact element carrier. Said flexible layer may be, for example, a gel layer. This flexibility allows compensation for minor irregularities in the cornea during contacting, so that the generated correcting cut surface has an extremely uniform profile without such irregularities.
In particular, a group of such described contact elements is provided, wherein all contact elements have a different design so as to allow different correcting cut surfaces to be generated.
Further, a method for producing a contact element as described above is provided, wherein the contact element is produced by material removal from a blank. Said material removal may be effected, for example, by means of diamond-turning, milling or ablation using laser radiation or by other methods. Of course, it is also possible to selectively apply or add material, respectively, to the blank so as to produce the contact element.
The blank may be, for example, a standard flap contact glass. Such standard flap contact glass may have, e.g. a spherically curved or a planar contact surface.
A contact element comprising the main part and the adapting element can be produced by mounting the adapting element to the main part. In particular, the second contact surface of the adapting element can be defined (e.g. by removing or applying material) before or after mounting to the main part.
There is further provided a method for generating a correcting cut surface in the cornea of an eye so as to correct ametropia by an apparatus comprising a laser unit, which can focus and move pulsed laser radiation in the cornea to generate a cut surface; a first contact element; and a control unit which controls the laser unit for generating a cut surface and comprises a standard control, which standard control would cause said standard cut surface in the cornea to have a known curvature with respect to a reference surface when a standard curvature is imposed upon the anterior corneal surface by the first contact element, wherein the curvature, with respect to the reference surface, of the correcting cut surface to be generated deviates from the known curvature of the standard cut surface which can be generated, and said method comprising the following steps: providing a second contact element adapted to generate the correcting cut surface; contacting the second contact element with the anterior corneal surface, whereby an actual curvature deviating from the standard curvature is imposed upon said surface, generating a cut surface using the standard setting, while the second contact element contacts the anterior corneal surface, in order to generate the correcting cut surface. This method allows to generate the desired correcting cut surface in a simple manner with great precision. In particular, a conventional laser keratome can be used to generate the correcting cut surface.
In the method, the second contact element may have the effect that, by the imposed actual curvature alone, the cut surface generated using the standard setting results in the correcting cut surface to be generated. Such contact element is particularly easy to produce. In particular, the second contact element can be provided such that the deviation between the actual curvature given by the second contact element and the standard curvature given by the first contact element corresponds to the deviation between the correcting and standard cut surfaces.
In particular, the second contact element can be provided as a one-part element. However, it is also possible for the second contact element to have a multi-part design. Thus, it may comprise a main part, having a first contact surface, and an adapting element, which is connected with the first contact surface and has a second contact surface facing away from the first contact surface and whose spatial shape is provided such that the actual curvature is imposed upon the anterior corneal surface.
In the method, the adapting element can be provided as a sheet or a lens.
Further, said method allows to separate a predetermined corneal lenticle within the cornea from the surrounding corneal tissue by generating a further correcting cut surface in addition to the generated correcting cut surface in that the anterior corneal surface is contacted by the first contact element or a third contact element, and then generation of a cut surface with the standard setting is carried out, in order to generate the further correcting cut surface. Both correcting cut surfaces together separate the volume of surrounding corneal tissue which corresponds to the corneal lenticle. The corneal lenticle is then removed from the cornea through an opening to the anterior corneal surface, such that both correcting cut surfaces contact each other and the anterior corneal surface thus has a modified curvature.
When generating the corresponding correcting cut surfaces in the cornea by the pulsed laser radiation, several processes initiated by the pulsed laser radiation take place in a time sequence within the tissue. If the power density of the radiation exceeds a threshold value during any pulse, an optical breakthrough forms which generates, for example, a plasma bubble in the cornea. The plasma bubble grows due to expending gas after the optical breakthrough has formed. If the optical breakthrough is not maintained, the gas generated in the plasma bubble is absorbed by the surrounding tissue and the bubble disappears again. Tissue-separating effects acting without a plasma bubble are also possible. For the sake of simplicity, all such processes, including their effects, are summarized herein by the term “optical breakthrough”.
In order to separate tissue, the laser radiation is applied in pulsed form, with the pulse duration usually being less than 1 ps. Thus, the power density required for the respective pulse to initiate the optical breakthrough is achieved within a small spatial region. High focusing of the laser beam in combination with the short pulses allows to insert the optical breakthrough in the cornea with pinpoint accuracy. In order to generate a cut, a series of optical breakthroughs is generated at the locations predetermined by the standard setting in combination with the corresponding contact element such that the desired correcting cut surface is formed thereby.
It is evident that the features mentioned above and those mentioned below, which are yet to be explained, can be used not only in the combinations mentioned, but also in any other combinations, or alone, without departing from the scope of the present invention.